“Our findings provide evidence that poor sleep may contribute to brain aging,” explains Abigail Dove, a neuroepidemiologist at the Karolinska Institute in Sweden, and points to inflammation as one of the underlying mechanisms.
High correlation with night-owl lifestyle and snoring
Researchers assessed 27,500 middle-aged and elderly people (average age 54.7 years) enrolled in the UK Biobank (a research institution conducting long-term follow-up studies of genetic predisposition and lifestyle effects on disease) to assess their sleep quality across five dimensions. About nine years later, they scanned the participants’ brains with MRI and used machine learning models to estimate their biological brain age.
Researchers determined sleep quality based on chronology (morning or evening), sleep duration, presence or absence of insomnia, presence or absence of snoring, and daytime sleepiness. Using these data, they classified participants into three sleep patterns, finding that 41.2 percent had healthy sleep, 3.3 percent had markedly poor sleep, and 55.6 percent fell into the middle group.
The analysis showed that for each point decrease in healthy sleep scores, the difference between brain age and chronological age increased by about six months. The group with the worst sleep quality showed that their brains were about a year older than their chronological age. This suggests that differences in sleep duration and sleep habits can significantly influence the rate of brain aging.
Researchers have found that all-night lifestyles, unhealthy sleep duration (more than 7-8 hours), and snoring habits are particularly strongly associated with brain aging. They also found that the five factors that determine sleep quality interact with each other. For example, insomnia can lead to excessive daytime sleepiness, and nocturnal lifestyle can lead to reduced sleep time.
Poor sleep leads to chronic inflammation in the body
To understand the mechanism by which poor sleep affects the brain, the research team also measured levels of low-grade inflammation in the body. Specifically, they used a combination of biomarkers, such as C-reactive protein levels, white blood cell and platelet counts, and the ratio of granulocytes to lymphocytes (a type of white blood cell) to analyze the role of inflammation in the relationship between sleep patterns and brain aging.
The results confirmed that higher levels of inflammation in the body increase brain aging. Mediation analysis (a method of analyzing the effect of intermediate variables in the causal relationship between two variables) found that inflammation explained about 7 percent of the association between intermediate sleep patterns and brain aging, and more than 10 percent of the association with poor sleep patterns. In other words, it is highly likely that poor sleep quality facilitates chronic inflammation in the body, which in turn accelerates brain aging.
Besides inflammation, there are several other ways that poor sleep can negatively impact the brain. First, its negative effect on the glymphatic system, which removes waste products from the brain primarily during sleep. If toxins in the brain are not removed efficiently during sleep, it can impair the function of nerve cells in the long run. Researchers have also reported that poor sleep can worsen cardiovascular health, which indirectly affects blood flow and tissue damage in the brain.
This story originally appeared in WIRED Japan and has been translated from Japanese.
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